Acute effects of hypoxia above 23,000 ft (unacclimatized person)

Coma and death

One of the most impt effects of hypoxia

The principal means by which acclimatization comes about

1. Great increase in pulmonary ventilation2. Increased nummbers of rbc3. Increased diffusing capacity of the lungs4. Increased vacularitu of the tissues5. Increased ability of the tissue cells to use oxygen despite low PO2

Increased alveolar ventilationto a maximun of abt 1.65 times normal

What effect would the immediate increase in pulmonary ventilation on rising altitude have on PCO2 and body fluid pH?

Large quantities of CO2 are blown off,reducing the PCO2, &increasing the pH of the body fluids

*these changes inhibit the brain stem respiratory center and thereby oppose the effect of low PO2 to stimulate respiration by way of the peripheral arterial chemoreceptors in the carotid and aortic bodies. Ensuing 2-5 days this inhibition fades away, and ventilation increases to 5x normal

19

The kidneys respond to decreased PCO2 by what mechanism?

Reducing hyrogen ion secretion and increasing bicarbonate excretion

20

The principal stimulus for causing an increase in rbc production

Hypoxia

21

The normal diffusing capacity for oxygen thru the pulmonary membrane

21 mL/mmHg/min

22

What factors increase the diffusing capacity for oxygen (after acclimatization)

Peripheral circulatory system changes during acclimatization

- Increased CO to as much as 30% but decreases back to normal in weeks as the blood hct increases- growth of increased numbers of systemic circulatory capillaries in the nonpulmonary tissues/ increased tissue capillary (angiogenesis) - also in active tissues exposed to chronic hypoxia

Work capacity is _________ (reduced/increased) in direct proportion to the decrease in maximum rate of oxygen uptake that the body can achieve

Reduced

26

Acute mountain sickness and high altitude pulmonary edema

Two events that happen when some people ascend rapidly to high altitudes ( begins from a few hours up to about 2 days)

1. Acute cerebral edema2. Acute pulmonary edema

27

Believed to result ffom local vasodilation of the cerebral blood vessels, caused by the hypoxia

Acute cerebral edema

Dilation of the arterioles increases blood flow into the capillaries, thus increasing capillary pressure, which causes leak into the cerebral tissues

Can lead to severe disorientation and other effects related to cerebral dysfunction

28

Cause is still unknownSuggested answer: severe hypoxia causes the pulmonary arterioles to constrict potently; const is greater in some parts of the lungs; capillary pressure in these areas become especially high and local edema occurs

Acute pulmonary edema

Allowing person to breathe oxygen usually reverses the process within hours

29

Chronic mountain sickness

When a person remains at high altitude for too long

1. The red cell mas and hct become exceptionally high 2. The pulmonary arterial pressure becomes elevated (even more than normal during acclimatization)3. Right side of the heart becomes greatly enlarged4. Peripheral arterial pressure begins to fall5. Congestive heart failure ensues6. Death, unless person is removed to a lower alt